How Underwater Tunnels Are Built?

Even though sailing on a boat can bring a fantastic experience, risks are often involved in the open waters. Boats are exposed to being engulfed by high tides and severe typhoons. In 1954, 5 ferries sunk into the waters of Tsugaru Strait which took a death toll of 1,150 lives.

Of course, many people were furious about the incident and one might also think that building bridges might be the solution but these typhoons will quickly crumble them to the ground. The Alternative solution to this problem will be one of the most terrifying ones which are to build an underwater tunnel below the sea.

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Despite the fear, an attempt was still made and in 1998, the Japanese government not only build one but it was also the deepest and longest underwater tunnel ever. The Seikan Tunnel was built 140 meters below sea level and measured 54 km long.

The question will be what is behind this magnificent engineering that is capable of preventing the mud and water from penetrating through the small holes of the tunnel.

The First Underwater Tunnel In The World

Thames Tunnel

The first underwater tunnel in the world was built below the Thames River in London. In the early 19th century, London was the pioneer in trading all over Europe, and the globe. The harbors were very pact with ships carrying coals and other merchandise on top of the roads full of carriages all around.

This congestion became much worst especially when the industrial revolution was at its peak. They needed a way to increase trading activities in London without adding any more pathways at the top.

The Use Of Tunnel Shield

Marc Brunel

At the time, the idea of building an underwater tunnel was considered insane and impossible to be done. However, an engineer realized that it will be the most effective solution if accomplished.

The risk is definitely there as the mud and water followed by the pressure can pass through the existing gaps and ultimately tear down the tunnel causing a catastrophe inside.

But in 1818, Marc Brunel known as England's best engineer created a smart device to realize this dream without letting any mud or water pass through. He uses what's called "tunnel shield" which is still being used to this day.

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It is basically a 40 feet submarine that is protected by walls of steel and 3 feet thick of bricks. It was then named Thames Tunnel which was built between Wapping and Rotherhithe.

The tunnel was not made by drilling through the ground but instead by using bare hands to chip the rocks and sand. As the shield moves forward, the workers at the front will start digging whereas the workers at the back will arrange the bricks along the tunnel that has just been dug.

The workers will have to work together by removing the mud and soil inside as well as the water. The work that usually takes 3 years became 18 years instead. Finally, the bricks will then be filled with concrete and the whole tunnel will be completed.

The tunnel today still plays a crucial role in the railway network of London Overground. For a short period of time, the tunnel was considered one of the wonders of the world.

Prefabricated Tunnel and Moles

By building a tunnel that was dug at the same time, it can also be built by building the tunnel first on the ground and later placed underwater. Usually, these tunnels are not built to completion but instead in several parts.

These segments will then be assembled to the vertical walls to ensure that it floats. With the help of additional weight, these segments will then sink and be placed in the tight and long cavity along the measured walls that were built.

This cavity was built by digging and ditch dredging before building the segments. Each segment will then be merged to form a tunnel. Water between the joints will be pumped out using a hydraulic system with the tunnels being soldered.

Ted Williams Tunnel

We give one example which is the Ted Williams Tunnel that connects the southern Boston part with the Logan Airport. It was built using the same technique as just explained and 12 segments each measuring 99 meters were assembled together to form this tunnel.

There is also a roadway built inside the tunnel. Despite this technique being more cost-effective, it definitely has its flaws. The first one is that the engineer will need to take extra precautions while sinking these segments as one error can cause a nightmare.

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Secondly, while the tunnel is being built under the ditch there is a possibility that several segments might be exposed to the water. The surfaces of the segment might cause an accident if it were to collide with a sinking ship or its anchor.

Thirdly, it brings a negative impact on the surrounding ecosystem as it was dug on the canal base.

Use of Tunnel Boring Machine(TBM)

The most simple method will be to use this huge drill to dig through the tunnel. The Strait Tunnel that connects the UK and northern France was built using heavy machinery known as Tunnel Boring Machine(TBM).

TBM which is also known as the mole is a machine that digs tunnels by cutting down hard rocks and stratum. But of course, this technique will come at a huge price as this machine will cost millions of dollars to own.

The Channel Tunnel in the UK requires 11 TBM to build. But even the choice of technique to build this tunnel depends on facilities, speed of the process, and cost, the most crucial aspect is the type of soil that must be penetrated.

With that being said, this technique might not be feasible and considered the best choice after all.

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